Process for reducing the tendency of electrostatic charging of photographic material



United States Patent 0 3,514,291 PROCESS FOR REDUCING THE TENDENCY OF ELECTROSTATIC CHARGING OF PHOTO- GRAPHIC MATERIAL Johannes Camiel Vanpoecke, Berchem, Lodewijk Felix de Keyser, Mortsel, and Luc Trudo Berben, Berchem, Belgium, assignors to Gevaert-Agfa N.V., Mortsel, Belgium, a Belgian company No Drawing. Filed Mar. 31, 1967, Ser. No. 627,320 Claims priority, application Great Britain, Oct. 4, 1966, 44,274/ 66 Int. Cl. G03c 1/82 US. Cl. 96-87 7 Claims ABSTRACT OF THE DISCLOSURE A process for reducing electrostatic charging of a photographic material comprising applying to the back side of the support a first layer comprising a mixture of (A) a partially neutralized copolymer of a hydrophobic monomer and a mono or dicarboxylic acid or half-ester or half-amide derivative thereof, and (B) a compatible hydrophobic polymer, and thereupon applying a protective layer of a non-tacky hydrophobic polymer.

It is known that photographic materials tend to be charged electrostatically. Such a charging can arise during any stage of the manufacture of the photographic material, especially on rewinding such material during the different steps of its manufacture as well as on rewinding during the cutting operation. Charging also occurs during unrolling in the photographic camera.

As the discharge of static electricity on the lightsensitive emulsion generates the known static markings or gives rise to an increased attraction of dust, it is required that these electrostatic charges are reduced or carried away as much as possible.

A new method has now been found according to which thetendency to electrostatic charging of photographic material is decreased to a low degree and according to which also after processing of the photographic material the antistatic properties are maintained.

According to the invention a process is provided for reducing the tendency to electrostatic charging of a photographic material comprising a support and at least one light-sensitive silver halide emulsion layer, which process comprises applying successively to the back side of the support a first layer comprising a mixture of (A) a partially neutralized copolymer of a hydrophobic a,,8- ethylenically unsaturated monomer and of an a,B-ethylenically unsaturated monoor dicarboxylic acid or derivative thereof, and (B) a compatible hydrophobic polymer, said layer being applied from a water-miscible organic solvent that affects the support, and thereupon applying a protective layer of a non-tacky hydrophobic polymer that does not interfere with the photographic properties of the silver halide emulsion layer.

The combination of an antistatic layer and of a hydrophobic protective layer confers excellent antistatic properties to photographic film manufactured on the basis of a cellulose ester support, such as cellulose triacetate, cellulose propionate, cellulose butyrate, and of cellulose mixed esters, such as cellulose acetate-butyrate. Although the further description is especially directed to photographic films having a cellulose ester support, the combination of antistatic layer and of hydrophobic protective layer can successfully be applied to other photographic supports, e.g. in the case of photographic paper which has been provided with a covering layer from a cellulose compound, such as nitrocellulose, cellulose esters or ethers, occasionally mixed with another hydrophobic polymer.

3,5 14,291 Patented May 26, 1970 The mixture forming the first layer adjacent to the cellulose ester support comprises a partially neutralized copolymer formed of hydrophobic and of hydrophilic monomeric units. The hydrophobic units derive from monomers capable of enhancing the sensitivity of the copolymer to organic solvents. In view of the above there can be included in the copolymer hydrophobic a,/3-ethylenical1y unsaturated monomers, such as styrene and its derivatives, e.g., nitrostyrene, and vinyl toluene, vinyl acetate, vinyl alkyl ethers, alkyl acrylates and alkyl methacrylates. The hydrophilic units originate from a,, 3-ethylenical1y unsaturated monoor dicarboxylic acids and their derivatives such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and citraconic acid, as well as their half-esters and half-amides. The copolymer is applied in its partially neutralized form which means that a sufficient amount of alkali metal hydroxide has been added to the copolymer in order to raise the pH to about 7.

The molecular Weight of the copolymer may vary Within very Wide limits, since in the case of the copolymer of styrene and maleic acid, similar results have been obtained with molecular weights varying between 10,000 and 350,000.

The above copolymer is mixed with a compatible hydrophobic polymer such as cellulose diacetate, cellulose propionate, cellulose butyrate, cellulose acetate-butyrate, hydroxyethylcellulose acetate, phenol-modified coumaronindene resin, poly(methyl methacrylate), and copolymers of styrene and allyl alcohol.

The hydrophobic copolymer, which can be regarded as the binding agent for the layer adjacent to the cellulose ester support, has to be soluble in a water-miscible organic solvent, which is able to affect the surface of the cellulose ester support as will be further explained hereinafter. Solvents, such as acetone, butanone, tetrahydrofuran and their mixtures occasionally also with water or methanol, are very suitable in the process of the invention.

To the first layer a protective layer of a non-tacky, hydrophobic polymer is applied, which firmly adheres to the first one, which does not interfere with the photographic properties of the light-sensitive silver halide emulsion layer, and which is resistant to abrasion during manipulation in the photographic apparatus. In fact any hydrophobic polymer can be employed when it satisfies the above enumerated criteria. Especially worth mentioning is the use of polymers such as cellulose diacetate, cellulose triacetate and copolymers of vinylidene chloride and acrylonitrile. In order to minimize the friction of the layer in the photographic apparatus, friction-reducing compounds such as waxes may be added to the layer composition.

A photographic film material is mainly composed of a cellulose ester support, a subbing layer and a light-sensitive silver halide emulsion layer. The object of the subbing layer is to firmly make adhere the hydrophilic lightsensitive layer to the hydrophobic support. The subbing layer always is applied from a solution in solvents which more or less affect the support surface.

By the term affecting is understood that these solvents attack the cellulose ester film superficially, and thereby modify the molecular structure of the support surface. As a consequence, after drying new tensile forces arise in that surface which tend to curl the photographic material.

If now to the back side of the support other layers are applied, one has to take care that under the influence of the treatment by solvents the tensile forces are compensated, which have arisen or shall arise by the application of the subbing layer and the light-sensitive emulsion layer to the front side of the support. This can be achieved by using as solvent for the first back-layer that kind of solvents which also attack the surface of the cellulose ester support.

According to the process of this invention a first layer is applied consisting of a mixture of partially neutralized copolymer and of a hydrophobic polymer that functions as binding agent for such copolymer. The mixture thus has to contain a certain amount of hydrophopic polymer, e.g. cellulose diacetate. Indeed, the hydrophobic polymer enhances the strength of the layer whereby its scratch resistance is increased and the deposition of dust from this layer onto the photographic apparatus during unwinding is diminished.

After a neutralisation to a pH of about 7 by means of an alkali metal hydroxide, the copolymer of hydrophobic monomer and of a,fl-ethylenically unsaturated monoor dicarboxylic acid forms a very effective antistatic the properties of which even after having been mixed with a hydrophobic binding agent are still sufficient. Normally, the antistatic copolymer is mixed with an equal or double amount of the hydrophobic binding agent to be worked up into a layer. The aqueous solution of the antistatic copolymer can be diluted with organic solvents, such as alcohols and ketones, by which mixing with the solution of the hydrophobic polymer is made possible.

In the case of the partially neutralized copolymer of styrene and maleic acid mixed with cellulose diacetate as binding agent, a good coating composition for the first layer is obtained by mixing:

50 ccs. of water 150 ccs. of methanol 800 ccs. of acetone 5 g. of cellulose diacetate, and 2.5 g. to 5 g. of copolymer.

The main purpose of the protective layer is to increase the scratch resistance of the material and especially to maintain the good electrostatic properties of the photographic material even after processing in the photographic baths, so that attraction of dust is strongly diminished also after processing. If less interest is taken in the antistatic properties of the processed material, occasionally the protective layer can be omitted. In such a case the electrostatic properties of the first layer would be lost by processing, such as usually is the case with the known antistatic layers. According to the invention, however, the second layer of hydrophobic polymer prevents the disappearance of the antistatic properties in the photographic baths, with the result that the finished photographic images will attract much less dust.

In the known methods the antistatic properties are mostly obtained by the use of hydroscopic products, which however have the disadvantage that they form sticky layers at higher values of relative humidity of the surrounding atmosphere. Since in the process of the invention the actual antistatic layer is covered with a hydrophobic layer, this disadvantage ceases to xist.

The combination of antistatic layer and of Protective layer according to the invention normally is applied to the photographic support before the light-sensitive silver halide emulsion layer or layers are coated. Indeed, the combination decreases the susceptibility of the material to be charged electrostatically. Hereby, the number of failures which could arise during the application of all further layers and during the rewinding in the different steps of manufacture and processing is greatly diminished. At the same time the deposition of dust onto the photographic material during these manipulations is decreased considerably.

The determination of the antistatic properties of the photographic material has been carried out by measuring the surface resistivity according to the method described in DIN 53,482 of October 1955. All the figures in the examples originate from measurements on the back side of the photographic material, i.e. on the side of the combination of antistatic layer and protective layer according to the invention.

The following examples illustrate the invention.

EXAMPLE 1 A film support of cellulose triacetate which has been coated on the front side with a known subbing layer, is coated on the back side with an antistatic layer in a proportion of 45 sq. m. per liter from the following solution:

Ccs. 20% aqueous solution of copoly (styrene/maleic acid) of molecular weight of about 30,000 and having been neutralized with sodium hydroxide to pH 7 12.5 Water 37.5 Methanol 150 Acetone L 700 5% solution in acetone of cellulose diacetate (degree of substitution of acetyl groups: 2.5) 100 After drying for 5 minutes at 70 C., a protective layer is applied thereto in a proportion of 55 sq. m. per liter from the following solution:

Ccs.

5% solution in acetone of cellulose diacetate (degree of substitution of acetyl groups: 2.5) Acetone 770 Methanol 75 Butanol 75 After drying, a high-sensitive gelatino silver halide emulsion layer is applied to the subbing layer and dried.

The surface resistivity of the back side of this photographic material has been measured after having conditioned the material at 30 and 60% respectively of relative humidity before as well as after processing in the normal photographic baths.

Before processing:

30% RH 1.2 10 Q/10 sq. cm. 60% RH 0.014 10 Q/10 sq. cm. After processing:

30% RH 3.7 l0 S2/l0 sq. cm. 60% RH 0.046 l0 t2/10 sq. cm.

If according to this same method the surface resistivity on the back side is measured of an analogous photographic material but without antistatic layer and protective layer a value beyond 500x 10 S2/ 10 sq. cm. is obtained.

EXAMPLE 2 Example 1 is repeated but the antistatic layer now has been formed from the following solution in a proportion of 40 sq. m./ liter:

After drying, a protective layer as in Example 1 is applied to the antistatic layer and a photographic silver halide emulsion layer to the front side of the support. The values of surface resistivity are the following:

Before processing:

30% RH 0.85 10 SZ/10 sq. cm. 60% RH 0.01 X 10 t'l/10 sq. cm. After processing:

30% RH 4 10 Q/10 sq. cm. 60% RH 0.05 l0 S2/10 sq. cm.

These values remain about the same if the surface res stivlty 1s measured on a same material but carrying no llght-sensltive silver halide emulsion layer.

EXAMPLE 3 One side of a film support of cellulose acetate-butyrate having a substitution degree of acetyl groups of 2 and of butyryl groups of about 0.75 is provided with a subbing layer. Then the other side of the support is coated with an antistatic layer from the following solution in a proportion of 40 sq. m./ liter:

After drying, a protective layer is applied thereto in a proportion of 48 sq. m./liter from the following solution:

Ccs.

5% solution of cellulose diacetate of Example 1 in acetone 120 Acetone 805 Butanol 75 Then a highly sensitive gelatino silver haliide emulsion layer is applied to the subbing layer.

The following values of surface resistivity have been measured:

Before processing:

30% RH 0.06 Q/10 sq. cm. 60% RH 0.002X10 t1/10 sq. cm. After processing:

30% RH 0.21 X l0 fl/l0 sq. cm. 60% RH 0.008 10 Q/10 sq. cm.

EXAMPLE 4 Example 2 is repeated but as protective layer a coating is applied in a proportion of 46 sq. m/liter from the following solution:

Ccs.

10% solution of copoly(vinylidene chloride/acrylonitrile) (80/20) in butanone 50 Butanone 950 A solution of the above copolymer in acetone has a viscosity of 60 cps. at 24 C.

The finished photographic material possesses the following values of surface resistivity:

Before processing:

RH O.9 1O S2/1O sq. cm. 60% RH 0.016 10 /10 sq. cm. After processing:

30% RH 2.1 X 10 Q/10 sq. cm. 60% RH 0.04X 10 t2/l0 sq. cm.

EXAMPLE 5 A cellulose triacetate support is provided with a subbing layer. Then the other side of the support is coated with an antistatic layer from the following solution in a proportion of 44 sq. m./1iter:

Ccs. 20% aqueous solution of copoly(styrene/maleic acid) with a molecular weight of about 45,000 and having been neutralized to pH 7 by means of sodium hydroxide 12.5 Water 12.5 Methanol 175 Acetone 700 5% solution of hydroxyethylcellulose acetate (degrees of substitution of acetyl and hydroxyethyl groups: 2.8 and 0.92 respectively) in acetone 100 6 After drying for 5 minutes at 70 C., the following protective layer is applied thereto from the following solution in a proportion of 48 sq. m./ liter:

Ccs.

5% solution of the above hydroxyethylcellulose acetate in acetone Acetone 750 Methanol 75 Butanol 75 After drying, a light-sensitive gelatino silver halide emulsion layer is applied to the subbed side of the support.

The following values of surface resistivity have been obtained for this material:

Before processing:

30% RH 1.1 X 10 t2/10 sq. cm. 60% RH 0.016 10 Z/l0 sq. cm. After processing:

30% RH 3.10 10 Z/10 sq. cm. 60% RH 0.052 10 t2/10 sq. cm.

EXAMPLE 6 To a support of cellulose triacetate an antistatic layer is applied from the following solution in a proportion of 44 sq. m./liter:

Ccs.

20% aqueous solution of copolymer of Example 3 12.5

Water 37.5

Methanol Acetone 700 5% solution of copoly(styrene/ally1 alcohol) (70/ 30) in acetone 100 After drying for 5 minutes at 70 C. the protective layer of Example 4 is applied thereto. After coating on the subbing layer a light-sensitive silver halide emulsion layer the photographic material obtained is measured as to its surface resistivity. The following values have been obtained.

Before processing:

30% RH 0.85 10 Q/10 sq. cm. 60% RH 0.014 10 t2/10 sq. cm. After processing:

30% RH 3.4x l0 Q/10 sq. cm. 60% RH 0.04 10 t2/l0 sq. cm.

EXAMPLE 7 To the back side of a cellulose triacetate film the front side of which has been provided with a known subbing layer, an antistatic layer is applied from the following solution in a proportion of 41 sq. m./ liter:

Ccs.

20% aqueous solution of the copolymer of Example 1 17.5 Water 32.5

Methanol 150 Acetone 750 10% solution of phenol-modified coumaron-indene resin in acetone c 50 After drying for 5 minutes at 70 C., a covering layer is applied thereto from the following solution in a proportion of 52 sq. m./liter:

Ccs.

5% solution of cellulose triacetate in a mixture of methylene chloride and ethanol (9/1) 100 Methylene chloride 810 Ethanol 90 The material is then provided with a light-sensitive gelatino silver halide emulsion layer. Measuring of the surface resistivity yields the following values:

Before processing:

30% RH 0.8 10 Q/10 sq. cm. 60% RH 0.011 1O t2/10 sq. cm.

7 8 After processing: resistivity of the photographic material obtained yielded 30% RH 3.10 l i2/ 10 sq. cm. the following results: 60% RH 0.O55 10 i2/1O sq. cm.

I Before processing: Even without the light-sensitive gelatino silver hal de RH 10 /10 cm. emulsion layer about the same values of surface reslstivity 5 RH OO24 10109/ cm have been measured. Aft processing:

, 30% RH 0.94Xl0 Q/10 sq. cm. EXAMPLE 3 60% RH 0.012 10 o/10 sq. cm.

A determined length of the photographic film of Exam- 10 What We claim is:

ple 1 is cut and perforated as is usually don f h 1. Process for reducing the tendency to electrostatic manufacture of cinematographic film. A length of about charging of a Photographic material Comprising a P- 6 to 7 f h fil h b i d i processed i th port and at least one light-sensitive silver halide emulnormal photographic baths. After having been dried, both SiOn ye hich Comprises applying successively to the ends of the film are spliced so that a loop is obtained. back slde the pp a first layer comprlsing a ix- Then this loop is placed in a usual copying apparatus ture of a p i y heutfallled copolymer of a yand continuously printed 300 times on cinematographic droph ,5-? Y Y unsaturated n0mer and of positive film. After 1, 100, 200 and 300 prints, the material hl t f y unsaturated 1110110- diCE-FbOXYIiC is controlled as to scratches and deposition of dust. As F 0T derlvatlve thereof Selected from the group @011- a comparison a cinematographic film is taken having the slsthlg 0f half-ester and m and (i a comsame support and the same silver halide emulsion as in Pfltlhle y ph h p ymer, sald layer belng applied Example 1 but carrying no antistatic layer d no from a water-nusclble organic solvent that affects the celtective layer. The results of the measurement are given in 1111056 ester pp t, h r by odifying the molecular the following table. structure of the support surface and thereupon a protective After the 1st; print After the 100th print After the 200th print After the 300th print Dust Scratches Dust Scratches Dust Scratches Dust Scratches Comparison 2 2 4 4 4 4 4 4 Film withdantisttattic 1 er an r0 ec ive lager. 1 1 1 1-2 1-2 2 2 2 The significances of the above figures in the examples layer of a non-tacky hydrophobic polymer that does not are the following: interfere with the photographic properties of the silver Soratching halide emulsion layer.

0: no scratching 2. Process according to claim 1, wherein the partially a very li l scratching neutralized copolymer is a copolymer of styrene and 2; a degree of sgratching hi h i t hindering f maleic acid, which has been partially neutralized with an photographic purposes alkali metal hydroxide to pH 7.

3: a degree of scratching which is hindering for photo- Pmcess according t Claim wherein the partially graphic purposes neutralized copolymer is a copolymer of vinyl methyl 4: a degree of scratching whereby the photographic mateether and l acld Whlch has been paltlany neutralized rial is not usable at an with an alkali metal hydroxide to about pH 7.

4. Process according to claim 1, wherein the com- Dust patible hydrophobic polymer is taken from cellulose di- 0: no dust acetate, hydroxyethyl cellulose acetate, a copolymer of 1: avery small quantity of dust styrene and allyl alcohol, and a phenol-modified cou- 2: a quantity of dust which is not hindering for photomaron-indene resin.

graphic purposes 5. Process according to claim 1, wherein the protective 3: a quantity of dust which is hindering for photographic layer is formed from the group consisting of cellulose purposes dlacetate, cellulose triacetate, hydroxyethyl cellulose ace- 4: a quantity of dust whereby the photographic material a a d a copo ymer of vinylidene chloride and acrylois not usable at all. nrtrile.

6. Process according to claim 1, wherein the photo- XAMPLE 9 graphic support is a cellulose ester support.

7. A light-sensitive material comprising a support and To the back side of a subbed cellulose triacetate film at least one light-sensitive silver halide emulsion layer an antistatic layer is applied from the following solution on one side, and on the back side of the support a first in a proportion of 48 sq. m./liter: layer comprising the dried residue of a mixture of (A) Ccs. a patrially neutralized copolymer of a hydrophobic afi- 10% aqueous copoly(vinyl methyl ether/maleic acid) ethylenically unsaturated monomer and of an age-ethylwith a molecular weight of about 250,000 and havenically unsaturated monoor dicarboxylic acid or derivaing been neutralized to pH 7 by means of potastive thereof selected from the group consisting of halfsium hydroxide 50 ester and ha f-a id and (B) a compatible hydrophobic Methanol 250 p ym r, i layer b ing applied from a water-miscible Acetone 600 g ic solvent that afiects the cellulose ester su port, 5% solution of cellulose diacetate of Example 1 in hereby modifying the molecular structure of the supacetone 100 p d thereupon a protective layer of a non-tacky hydrophobic polymer that does not interfere with the photographic properties of the silver halide emulsion layer.

After drying for 6 minutes at 70 C., a protective layer is applied thereto as in Example 3. 'Ihereupon the front side of the material is coated with a photographic gelatino silver halide emulsion layer. Measurements of the surface 7 (R f r on f ll i page) 9 10 References Cited 3,033,679 5/1962 Laakso et 211. 96-87 UNITED STATES PATENTS 3,039,870 6/1962 Laakso et a1. 9687 2074 47 3 1 37 Hagedorn et 211' P. RONALD H. SMITI'I, Pnmary Examlner 2,973,263 2/1961 Kaszuba et a1. 9687 US. Cl. X.R.

2,984,568 5/1961 Hart et a1 96-87 XR 

